One of the important fission products present in waste solutions resulting from the chemical reprocessing of nuclear fuels is cesium-137. Minor amounts of the Cs-134 isotope are also present in these solutions. The cesium-137 is highly radioactive and, as part of the waste management program, it is desirable to separate it from other, non-radioactive or less radioactive, constituents. One method that has been employed is precipitation from alkaline solutions by the addition of a soluble nickel, zinc, cupric, cobaltous, cadmium, uranyl, or manganous salt, and potassium ferrocyanide. This gives a complex ferrocyanide precipitate containing cesium, which may be represented by the general formula .sup.134-137 Cs.sub.a M.sub.b . [Fe(CN).sub.6 ].sub.c . xH.sub.2 O, where M represents Ni, Zn, Cu, Fe, Co, Cd, UO.sub.2 or Mn; a, b, and c are integers; and x is zero or a small number. A particularly important precipitate of this class is cesium nickel ferrocyanide, which is stored in large quantities in underground tanks at the Hanford Works located near Richland, Washington, USA. See U.S. Pat. No. 2,769,780, granted Nov. 6, 1956, to W. E. Clifford and R. E. Burns, and U.S. Atomic Energy Commission Reports TID-7515 (p. 290) and HW-70874.
By various methods, it is possible to recover the cesium from this precipitate. However, the supply of cesium-137 available far exceeds the present demand for industrial uses. The precipitate is slightly soluble and, because of its finely divided, and high surface area character, might present some hazard if it should escape. It is therefore desirable to be able to convert the ferrocyanide to an immobile, less soluble product. The ferrocyanide precipitation process is also in use at other locations in various countries. Many locations lack the favorable geological and climatic conditions of Hanford for the storage of radioactive wastes and for those sites the conversion to a less mobile, less soluble product is still more desirable.
Prior publications have shown the use of basalt to form glasses with nuclear wastes in which fission products, including cesium-137, are immobilized. See "The Endothermic Process - Application to Immobilization of Hanford In-Tank Solidified Waste," by Michael J. Kupfer and Wallace W. Schulz, U.S. Atomic Energy Commission Report ARH-2800.
Incorporation of radioactive wastes in soda-lime glass prepared from sand, lime, and sodium carbonate is also known.
However, no previous work of which we are aware solves the problem of the immobilization of the complex cesium ferrocyanides and it is the object of our invention to provide a process for incorporating those compounds in a dense, insoluble glass.